Mapping the dextran sulfate binding site on CD2

Summary This study has analysed the binding of a series of anti‐CD2 monoclonal antibodies (MoAbs) to T cells in the presence of the sulfated polysaccharide dextran sulfate (2·3 sulfates/monosaccharide, 500 kDa) (DXS) to define the DXS binding site on CD2. The results show that DXS interacts primarily at the T11 2 epitope. Thus five anti‐CD2 MoAbs which bound to the T11 2 epitope were inhibited in their binding by DXS. In contrast, seven anti‐CD2 MoAbs that totally inhibited sheep red blood cells (SRBC) rosetting (identifying the T11 1 epitope) were unaffected in their binding to T cells in the presence of DXS. Three MoAbs which partially inhibited SRBC rosetting and thereby defining only part of the T11 1 epitope, were also inhibited in their binding by DXS. Consistent with the conclusion that the DXS binding site on CD2 is associated with the T11 2 epitope was the observation that interaction of DXS with CD2 resulted in augmented binding of the four MoAbs defining the T11 3 epitope, possibly reflecting an increased expression of the T11 3 (activation, CD2R) epitope of CD2. Collectively, the data presented support the notion that a natural ligand for the T11 2 epitope of CD2 will be identified as a sulphated carbohydrate structure.